High voltage regulator

ABSTRACT

A horizontal flyback transformer in a television receiver includes a driving choke winding coupled to a horizontal drive stage. A regulating winding is wound on the same core leg as the driving choke winding. A high voltage winding and a primary winding for driving a horizontal deflection yoke coil are wound on an opposite core leg. To regulate the high voltage developed by the high voltage winding, the regulating winding is coupled to a variable loading circuit controlled by current through a resistor in series with the driving choke winding. Each core leg includes an air gap selected to cause the leakage inductance between the primary winding and the driving choke winding to be equal to the inductance of the primary winding.

United States Patent 1191 McLeod, Jr.

[111 3,824,427 1451 July 16, 1974 HIGH VOLTAGE REGULATOR [75] lnventor:' Fenwick R. McLeod, Jr., Prospect Heights, [11. [73] Assignee: Warwick Electronics Inc., Chicago,

Ill.

[22] Filed: Mar. 16, 1973 [21 Appl. No.: 342,313

52 us. c1. 315/29 [51] Int. Cl. H01j 29/70 [58] Field of Search 315/28-29, 315/27 SR, 27 TD, 23, 24, 27 R [56] References Cited UNITED STATES PATENTS 3,517,253 6/1970 Dietz 315/27 R 3,519,741 7/1970 Knight.. 315/27 R 3,609,447 9/1971 'Hirota.. 315/27 TD 3,721,858 3/1973 Shimizu 315/29 HORZ. DRIVE Primary Examiner-T. H. Tubbesing Assistant Examiner-J. M. Potenza Attorney, Agent, or Firm-Hofgren, Wegner, Allen, Stellman & McCord ABSTRACT A horizontal flyback transformer in a television receiver includes a driving choke winding coupled to a horizontal drive stage. A regulating winding is wound on the same core leg as the driving choke winding. A high voltage winding and a primary winding for driving a horizontal deflection yoke coil are wound on an opposite core leg. To regulate the high voltage developed by the high voltage winding, the regulating winding is coupled to a variable loading circuit controlled by current through a resistor in series with the driving choke winding. Each core leg includes an air gap selected to cause the leakage inductance between the primary winding and the driving choke winding to be equal to the inductance of the primary winding.

21 Claims, 10 Drawing Figures PAIENTEnJuusmu 3.824427,

SHEET 1 OF 3 HORZ. DRIVE PATENTED JUL 1 61974 sum 2 or 3 SW.I

DI 3 l r if? FEEDBACK CIRCUIT l l l L 1 HIGH VOLTAGE REGULATOR BACKGROUND OF THE INVENTION This invention relates to a horizontal flyback transformer and associated regulating circuit.

,To regulate the high voltage output from a horizontal flyback transformer, it has been known to provide a regulating winding coupled to a regulating circuit which produces variable loading under control of a sensed characteristic. Typically, the auxiliary or regulating winding is located on the same core leg of the flyback transformer as is the high voltage winding. Examples of such prior systems are illustrated in the U.S. Pats. to Schade No. 2,843,796, Shulman et al. U.S. Pat. No. 3,134,045, and Knight U.S. Pat. No. 3,519,741. While the use of a regulating winding satisfactorily controls the high voltage output, prior systems have required a large driving current from the horizontal output stage.

The value of leakage inductance between various flyback windings has been used for regulation and to control the harmonic tuning of the high voltage circuit. The leakage inductance of a transformer is equal to the number of leakage flux linkages per unit of current, and

is approximately constant despite the nonlinearities involved in self inductance and mutual inductance as a function of flux or current. Leakage flux links only a particular winding, as distinguished from mutual inductance which links a plurality of windings. The leakage inductance between the high voltage or tertiary winding and the primary winding has been adjusted for harmonic ringing, as shown for example by U.S. Pat. to Brooks No. 3,132,284. However, between the other windings of a flyback transformer, the leakage inductance is generally designed to be as small as possible, as indicated by U.S. Pat. to Rietveld et al. No. 3,500,116,

' Harmonic tuning of the high voltage winding has also been utilized to increase high voltage. The above noted Rietveld et al. U.S. Pat. No. 3,500,l l6 utilizes fifth harmonic tuning. The above noted Brooks U.S. Pat. No. 3,132,284 utilizes third harmonic ringing to get increased high voltage, by controlling the leakage inductance between the high voltage or tertiary winding and the primary winding.

I SUMMARY OF THE INVENTION primary winding. Unlike prior flyback transformers in which the leakage inductance is generally selected to be as low as possible, the above noted leakage inductance is desirably made equal to the inductance of the primary winding. The value of the leakage inductance is controlled by the use of air gaps and coil turns. The flyback transformer also incorporates various techniques to control harmonic tuning of the high voltage circuit.

One object of the present invention is the provision of an improved horizontal flyback transformer having a regulating winding'located on a core leg opposite a core leg carrying a high voltage winding and/or a deflection winding.

Another object of this invention is the provision of a horizontal flyback transformer which controls leakage inductance by the use of air gaps in the core legs and coil turns, and desirably makes the leakage inductance equal to the inductance value of one of the windings.

Other advantages and features of the invention will be apparent from the following description, and from the drawings. While an illustrative embodiment of the invention is shown 'in' the drawings and will be described in detail herein, the invention is susceptible of embodiment in many different forms and it should be understood that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS .FIG. 1 is a schematic diagram of a novel horizontal flyback transformer and associated regulating circuit, as incorporated in the horizontal stage of a television receiver;

FIG. 2 diagramatically illustrates the mechanical construction of the novel horizontal flyback transformer;

FIG. 3illustrates a simplified equivalent circuit of the applicants horizontal flyback transformer and regulating circuit;

FIG. 4 illustrates a detailed equivalent circuit of the applicants horizontal flyback transformer and regulating circuit;

FIGS. 5A, 5B, 5C, 5D, and 5E illustrate current and voltage waveforms at various locations in the circuits of FIGS. 3 and 4; and

FIG. 6 is a graph of voltage versus current for the high voltage or tertiary winding of the flyback transformer, illustrated for several values of leakage inductance.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning to FIG. 1, the horizontal output stage of a television receiver is illustrated, including a horizontal flyback transformer 20 carrying at least four windings W. A horizontal driving or choke winding W provides horizontal scan current to the flyback transformer and is driven by the horizontal output of a switch SW1 controlled by a horizontal drive output stage 22. A deflection of primary winding W provides horizontal scan current to a horizontal deflection coil or yoke winding W which is associated with the image reproduction device, as a cathode ray tube (CRT) 24. A tertiary or high voltage winding W produces high voltage pulses which are rectified by a high voltage diode D2 for coupling to the high voltage HV anode of the CRT 24.

To regulate the value of high voltage, a regulating winding W is coupled to a variable loading or regulating circuit 26 which variably clamps the regulating winding W The variable damping is controlled by a feedback circuit 28 which is coupled to a sensing resis- 3 tor R3 located in series with the driving choke winding W The mechanical construction of the horizontal flyback transformer 20 is illustrated in FIG. 2. The ends of a C-shaped ferrite core 30 are spaced from the ends of a C-shaped ferrite core 31 so as to produce a pair of air gaps G in an otherwise closed magnetic loop. The air gap which spaces the pair of facing ends in a low voltage leg 33 of the magnetizable core is designated G Conversely, the air gap which separates the facing ends of a high voltage leg 34 is designated G On low voltage leg 33, the driving choke winding W,- and the regulating winding-W are concentrically wound. On the high voltage leg 34, the primary winding W is wound in a known manner. The high voltage winding W is concentrically wound over the primary winding W and may be spaced therefrom by an insulating spacer, in order to control the leakage inductance between windings W,,, and W and to insulate the high voltage winding W from winding W The leakage inductance of windings located on opposite core legs is controlled by the spacing of the air gaps G and coil turns.

The operation of applicants flyback transformer and regulating circuit may be understood with reference to the simplified equivalent circuit shown in FIG. 3. All inductances L carry a subscript to identify the particular winding W which is represented by that inductance value. Thus Ly represents the yoke inductance, L represents the primary winding inductance, and L represents the driving choke winding inductance.

L represents the leakage inductance between windings W and W The flyback transformer 20 is purposely designed to have a large leakage inductance Lp and preferably of a value equal to the inductance LP. The value of the leakage inductance in turn is controlled by the physical dimensions of the flyback transformer, including the spacing of the gaps G and coil turns, which illustratively may be 0.030 inches.

The remaining components of the equivalent circuit of FIG. 3 are an S-shaping capacitor C2, and a voltage supply V. A switch SW1 periodically opens and closes at a rate determined by the horizontal driving frequency. The circuit functions as follows. During the horizontal trace interval, switch SW1 is closed and current flows from the voltage source V through L and L At the beginning of the horizontal retrace interval, SW1 is open and the energy stored in L during the trace interval by inductive coupling from L, is transferred to capacitor 52 and back to L with polarity reversed by retrace tuning.

Referring to FIG. A, the horizontal driving current I through L is represented by ILP-TI'IIS current consists of a sawtooth wave including a trace portion 40 and a retrace portion 42. The current through II' causes the yoke current to be of proper form to horizontally deflect the electron beam of the CRT in order to form a raster.

In a conventional flyback transformer, the winding W is normally tightly coupled to winding W and hence the current through L is normally substantially the same as through L However, in applicants circuit, the leakage inductance L is selected to be substantially higher than normal, and preferably equal to L This causes a substantially constant current I in coil L as represented by the current curve ILC in FIG. 58. It has been determined empirically that the closer inductance L approaches inductance L the more steady is the current flow in winding W This steady current flow in turn represents minimum energy requirements for maintaining current flow in the driving choke winding, and thus serves to lower the energy requirements of the flyback transformer and associated circuits.

In FIG. 4, the equivalent circuit of FIG. 3 has been expanded to illustrate further components. L represents the inductance of the tertiary or high voltage winding, and L represents the leakage inductance between the windings L and L The leakage inductance L is controlled by the spacing between the concentrically woundcoils W and W Capacitance Cp represents the distributed capacitance of coil W To increase high voltage, natural transformer tunings are resonated at the third harmonic frequency of the retrace period. The circuit is then mistuned by capacitor 52 to the high frequency side by a slight amount, L and C, are resonated at the third harmonic frequency of the retrace period. The voltage across L is shown in FIG. 5E and V .The leakage inductance L rings at the third harmonic frequency of the retrace period, as illustrated in FIG. 5D. The voltage VLPH adds to the voltage across L illustrated by the dotted line in FIG. 5E, so as to produce the resultant shown by the solid line in FIG. 5E. The dotted line in FIG. 5C represents the voltage which would occur across L without the ringing effect of L Returning to the equivalent circuit of FIG. 4, D2 represents the high voltage diode coupled to the high voltage winding W Capacitor C represents the filter capacitance for the high voltage supply, and resistance R,,,- represents the resistance of the high voltage load. Both components C and R include lumped circuit components located between diode D2 and the CRT anode, as well as internal and distributed components associated with the CRT.

In the equivalent circuit, a sensing resistor R3 is located to produce a feedback voltage which is sensed by a feeback circuit 28. The output of the feedback circuit 28 controls a variable resistor R1 which is located in a regulating network 26 which includes a capacitor C 1, an inductance L of the regulating winding W and a diode D1. The regulating network 26, under control of the feedback circuit 28, acts as a variable load which maintains a constant high voltage despite changes in beam current in the CRT.

Unlike prior circuits, the regulating winding W is located on the LV side of the flyback transformer 20, see FIG. 2, reducing the driving current requirements. The voltage developed across current sensing resistor R3 is due to the current ILC' shown in FIG. 5B. This sensing or feedback voltage is utilized to vary the resistance of R1. The resulting regulation characteristic of the circuit is illustrated in FIG. 6. As leakage inductance L approaches in magnitude inductor L the regulation approaches the horizontal line shown at 25 kilovolts. Thus, excellent regulation characteristics are produced by controlling the spacing of the air gaps G the coil turns and the other mechanical dimensions of the flyback transformer 20 so as to have L equal to L Returning to FIG. I, the components which produce the equivalent circuit of FIG. 4 will now be described in detail. The driving choke winding W is divided into two portions, with switch SW1 being located between a section top W and a bottom section W The switch SW1 takes the form of a transistor 50 and damper diode 51 coupled across a retrace capacitor 52 which is located between coils W and W The retrace capacitor 52 has a value which controls the third harmonic tuning.

Coil W is coupled between a source of positive DC potential, or 8+, and one side of the retrace capacitor 52. The lower coil W is coupled between the opposite side of retrace capacitor 52 and through sensing resistor R3 to a source of reference potential or ground 60. Capacitor C2 forms the S-shaping capacitor for the horizontal yoke coil W Primary coil W is coupled through a horizontal centering network 54 to the horizontal yoke coil W Additional centering and other correction networks, such as for pincushion and the like (not illustrated), may be associated with horizontal yoke coil Wy, as desired. For clarity, the additional correction circuits are not illustrated in FIG. 1.

Drive currentthrough the coils W passes through resistor R3, and the voltage drop thereacross is coupled to a transistor 62 in the feedback circuit 28. Transistor 62 is DC coupled to transistor 64, which forms resistance R1. The value of resistance, as controlled by the biasing of transistor 62, controls the damping or variable loading provided by regulating coil W On the high voltage side of flyback transformer 20, the high voltage coil W is coupled through the parallel combination of a resistor 70 and capacitor 72 to ground 60, and through high voltage diode D2 to the anode ofthe CRT 24. A focus resistor 76 is located between the high voltage lead and ground 60. Additional components (not illustrated for clarity) may be provided as desired.

1. In a television receiver including horizontal scanning means having horizontal transformer with a driving winding coupled to a horizontal drive stage and a high voltage winding for developing a high voltage of varying current, a regulating system. comprising:

first and second core legs forming a transformer core for said horizontal transformer, said driving winding and said regulating winding being wound on said first core leg, said high voltage winding being wound on said second core leg, and e I circuit means for, variably loading the regulating winding to maintain the high voltage developed by said high voltage winding at an approximately constant level.

' 2. The regulating system of claim 1 wherein said circuit means includes sensing means for generating a sensing signal which varies with changes in high voltage current, and feedback means coupled between said sensing means and said regulating winding for variably loading the regulating winding in response to said sensing signal.

3. The regulating system of claim 2 wherein said sensing means comprises resistive means in series with said driving winding for developing thereacross a voltage drop corresponding to said sensing signal.

4. The regulating system of claim 3 wherein said feedback means comprises semiconductor means for establishing a variable resistance, first network means for coupling said resistive means to said semiconductor means to control the resistance thereof, and second network means for coupling said regulating winding to said semiconductor means.

5. The regulating system of claim 4'wherein said second network means comprises a diode poled to pass current flow in only one direction.

6. The regulating system of claim 1 wherein said driving winding is concentric with said regulating winding.

7. The regulating system of claim 6 wherein said horizontal transformer further includes a deflection winding coupled to a horizontal deflection coil, said deflection winding being wound on said second core leg and concentric with said high voltage winding.

8. The regulating system of claim 7 including control means for establishing between said driving winding and said deflection winding a leakage inductance of a value approximately equal to the inductance of said deflection winding.

9. The regulating system of claim 8 wherein said control means comprises a pair of air gaps respectively located in said first and second core legs.

10. In a television receiver including horizontal scanning means having a flyback transformer with a high voltage winding for developing high voltage of varying current and a deflection winding coupled to a horizontal deflection coil, a regulating system, comprising;

first and secondcore legs forming a transformer core for said flyback transformer, said high voltage winding and said deflection winding being wound on said second core leg,

a regulating winding wound on said first core leg, and

circuit means for variably loading the regulating winding to regulate the high voltage developed by said high voltage winding.

11. The regulating system of claim 10 wherein said high voltage winding is concentric with said deflection winding, and said flyback transformer includes a driving winding wound on said first core leg and coupled to a horizontal drive stage.

i 12. The regulating system of claim 11 wherein said circuit means includes a feedback resistor in series with said driving winding, and means responsive to the voltage drop across said feedback resistor for controlling a variable resistance in series with said regulating winding.

13. The regulating system of claim 12 wherein at least one of said core legs includes an air gap having a size to cause the leakage inductance between the driving winding and the deflection winding to be approximately equal to the inductance of the deflection windmg.

14. In a television receiver including a horizontal output stage, a horizontal deflection coil, and a horizontal scanning circuit for coupling the horizontal output stage to the horizontal deflection coil, the improvement comprising:

horizontal transformer means having a driving winding coupled to said horizontal output stage and a deflection winding coupled to said horizontal deflection coil, and

control means for establishing between said driving winding sand said deflection winding a leakage inductance of a value approximately equal to the inductance of said deflection winding.

15. The improvement of claim 14 wherein said horizontal transformer means has a magnetizable core generally forming a closed loop, and said control means comprises an air gap breaking the closed loop of the magnetizable core.

16. The improvement of claim wherein said magnetizable core comprises two sections each of generally C-shape and having a pair of ends, and said air gap comprises a pair of air gaps separating the spaced adjacent ends of the two sections.

17. The improvement of claim 16 wherein said magnetizable core includes first and second core legs with one of said air gaps being located in said first core leg and the other of said air gaps being located in said second core leg, said driving winding being wound about said first core leg and said deflection winding being wound about said second core leg.

18. The improvement of claim 17 wherein said horizontal transformer means includes a regulating winding wound on said first core leg, a high voltage winding wound on said second core leg, and circuit means for variable loading the regulating winding to maintain an approximately constant level of high voltage from said high voltage winding.

19. The improvement of claim 14 wherein said horizontal transformer means includes a regulating winding and a high voltage winding, magnetizable core means having at least a first core leg and a second core leg, said deflection winding being wound on said first core leg, and at least one other ofsaid windings being wound on said second core leg.

20. The improvement of claim 19 wherein said high voltage winding is wound on said first core leg and is concentric with said deflection winding, said regulating winding is wound on said second core leg, and said driving winding is wound on said second core leg and is concentric with said regulating winding.

21. The improvement of claim 20 wherein said control means comprises a pair of air gaps each located in a different one of said first and second core legs. 

1. In a television receiver including horizontal scanning means having horizontal transformer with a driving winding coupled to a horizontal drive stage and a high voltage winding for developing a high voltage of varying current, a regulating system, comprising: first and second core legs forming a transformer core for said horizontal transformer, said driving winding and said regulating winding being wound on said first core leg, said high voltage winding being wound on said second core leg, and circuit means for variably loading the regulating winding to maintain the high voltage developed by said high voltage winding at an approximately constant level.
 2. The regulating system of claim 1 wherein said circuit means includes sensing means for generating a sensing signal which varies with changes in high voltage current, and feedback means coupled between said sensing means and said regulating winding for variably loading the regulating winding in response to said sensing signal.
 3. The regulating system of claim 2 wherein said sensing means comprises resistive means in series with said driving winding for developing thereacross a voltage drop corresponding to said sensing signal.
 4. The regulating system of claim 3 wherein said feedback means comprises semiconductor means for establishing a variable resistance, first network means for coupling said resistive means to said semiconductor means to control the resistance thereof, and second network means for coupling said regulating winding to said semiconductor means.
 5. The regulating system of claim 4 wherein said second network means comprises a diode poled to pass current flow in only one direction.
 6. The regulating system of claim 1 wherein said driving winding is concentric with said regulating winding.
 7. The regulating system of claim 6 wherein said horizontal transformer further includes a deflection winding coupled to a horizontal deflection coil, said deflection winding being wound on said second core leg and concentric with said high voltage winding.
 8. The regulating system of claim 7 including control means for establishing between said driving winding and said deflection winding a leakage inductance of a value approximately equal to the inductance of said deflection winding.
 9. The regulating system of claim 8 wherein said control means comprises a pair of air gaps respectively located in said first and second core legs.
 10. In a television receiver including horizontal scanning means having a flyback transformer with a high voltage winding for developing high voltage of varying current and a deflection winding coupled to a horizontal deflection coil, a regulating system, comprising; first and second core legs forming a transformer core for said flyback transformer, said high voltage winding and said deflection winding being wound on said second core leg, a regulating winding wound on sAid first core leg, and circuit means for variably loading the regulating winding to regulate the high voltage developed by said high voltage winding.
 11. The regulating system of claim 10 wherein said high voltage winding is concentric with said deflection winding, and said flyback transformer includes a driving winding wound on said first core leg and coupled to a horizontal drive stage.
 12. The regulating system of claim 11 wherein said circuit means includes a feedback resistor in series with said driving winding, and means responsive to the voltage drop across said feedback resistor for controlling a variable resistance in series with said regulating winding.
 13. The regulating system of claim 12 wherein at least one of said core legs includes an air gap having a size to cause the leakage inductance between the driving winding and the deflection winding to be approximately equal to the inductance of the deflection winding.
 14. In a television receiver including a horizontal output stage, a horizontal deflection coil, and a horizontal scanning circuit for coupling the horizontal output stage to the horizontal deflection coil, the improvement comprising: horizontal transformer means having a driving winding coupled to said horizontal output stage and a deflection winding coupled to said horizontal deflection coil, and control means for establishing between said driving winding sand said deflection winding a leakage inductance of a value approximately equal to the inductance of said deflection winding.
 15. The improvement of claim 14 wherein said horizontal transformer means has a magnetizable core generally forming a closed loop, and said control means comprises an air gap breaking the closed loop of the magnetizable core.
 16. The improvement of claim 15 wherein said magnetizable core comprises two sections each of generally C-shape and having a pair of ends, and said air gap comprises a pair of air gaps separating the spaced adjacent ends of the two sections.
 17. The improvement of claim 16 wherein said magnetizable core includes first and second core legs with one of said air gaps being located in said first core leg and the other of said air gaps being located in said second core leg, said driving winding being wound about said first core leg and said deflection winding being wound about said second core leg.
 18. The improvement of claim 17 wherein said horizontal transformer means includes a regulating winding wound on said first core leg, a high voltage winding wound on said second core leg, and circuit means for variable loading the regulating winding to maintain an approximately constant level of high voltage from said high voltage winding.
 19. The improvement of claim 14 wherein said horizontal transformer means includes a regulating winding and a high voltage winding, magnetizable core means having at least a first core leg and a second core leg, said deflection winding being wound on said first core leg, and at least one other of said windings being wound on said second core leg.
 20. The improvement of claim 19 wherein said high voltage winding is wound on said first core leg and is concentric with said deflection winding, said regulating winding is wound on said second core leg, and said driving winding is wound on said second core leg and is concentric with said regulating winding.
 21. The improvement of claim 20 wherein said control means comprises a pair of air gaps each located in a different one of said first and second core legs. 